Telephone systems are known which provide a common interface between a plurality of users and a public telephone network. Such a PBX system includes a central box with line cards providing connections to assigned lines of a public telephone network. The central box is connected by wires such as twisted pair wires to individual telephone units. The connection from the central box to the telephone units may be by way of analogue or digital signals. More recently, digital signals are sent by the central unit to the phone units. The digital signals include voice data as well as control and messaging data. The units include a simple handset as well as a speaker for paging, intercom type communications and speaker phone applications. Typically the base unit also includes a microphone. The handset is a typical handset providing a speaker and a microphone.
Telephone systems using distributed networks, such as local area networks (LANs) are also generally known. With these systems, a distributed network is provided, such as carrier sense multiple access/collision detection (CSMA/CD, see IEEE 802.3) generally known as Ethernet. A telephone network system is provided with a central box having line cards connected to the distributed network as well as network devices connected to the network. The network devices include network telephones with, for example, a base unit with a speaker and a microphone and a handset (with a speaker and a microphone). Data packets are sent over the network between network devices. A network control processor or network call processor (NCP) may be used to monitor and control the access to the public telephone network. Features specific to the user may be established with the NCP.
Digital PBX systems and telephone systems using distributed networks are known which allow the users to provide a conference call. The conference call may be between users of the telephone system or between a user of the telephone system and telephone units connected through outside lines. Even when the conference call is set up using the telephone system, such past systems do not allow users to selectively drop participants in the conference call. In such systems, the originator of the conference call may at best be able to drop the last participant that was added. Further, people do not know who all of the memners are, on the call at any given moment. Conference call members tend to constantly ask who is on the call or is not etc. Some conference call systems notify the members that some user has just joined or departed a conference. However, this still makes it difficult to keep a track of the total member list.